For NVidia, I would stay with DX8.1b as they do not yet have any WHQL drivers for DX9, and limited hardware support.
This does not mean you cannot run DX9, but why risk it? It does not buy you anything at all.
The 30.82 drivers are still my best pick for NVidia cards. You can use the 41.09's as an alternative. They seem to be the only 4x.xx drivers that seem to do a fair job and are pretty stable.
I would definately shy away from 43.xx and 45.xx drivers. These wre primarily done for the NV3x based cards and introduce some rather odd graphic issues for other NVidia cards.
